We will expand our current retrospective cohort study to determine the effect of molecular and histologic factors on breast cancer risk in women with non-invasive breast disease. The study cohort will consist of 12,670 women with non-invasive breast disease diagnosed at our study hospitals between 1959 and 1991. Paraffin embedded tissue from their initial breast biopsies is available on these patients. To date, follow-up has been obtained on all patients biopsied before 1987. Follow-up to determine breast cancer diagnosis and other epidemiologic risk factors will be updated and extended through review of hospital and tumor registry records as well as interviews with these patients or their next-of-kin. We will conduct a series of nested case-control studies on these women. Approximately 455 cohort members will develop invasive breast cancer during follow-up. These women will be our case patients. Two controls will be selected for each case matched on entry histology, age at biopsy and year of biopsy. Our major goals are to determine the influence of various molecular factors on the breast cancer risk associated with different types on benign breast disease. These include abnormal expression or regulation of the extracellular matrix-degrading enzyme matrilysin, microsatellite instability and loss of heterozygosity in benign tumors, and several markers of intercellular adhesion, cell proliferation and angiogenesis. PCR methods will be used to determine microsatellite instability and loss of heterozygosity. Immunohistochemical and in situ hybridization methods will be used to study matrilysin and other proteins. Conditional logistic regression analysis will be used to assess the individual and combined effects of molecular, histologic and epidemiologic variables on breast cancer risk. This project will expand our repository of paraffin embedded breast cancer tissue on a large cohort of women with known outcome. It will permit the combination of modern methods in molecular biology, pathology and epidemiology to assess potentially powerful new markers of breast cancer prognosis, and may lead to important advances in the prevention and treatment of this disease.